Welding rods are known for joining plastic materials by welding. Such thermoplastic materials include polyethylene and the like. An illustrative welding rod type is described in Canadian Patent No. 1,235,872 and in Reissued Canadian Patent No. 1,325,092, and consists of a solid core of thermoplastic material wrapped with a helical winding of nichrome or stainless steel wire through which current is applied to soften and melt the plastic core and the contacting portions of the plastic members to be welded. These patents disclose that other forms of resistive elements such as coatings of suitable resistivity may be used, provided that the coating is compatible with the thermoplastic core.
However, it has been found that such a welding rod is not altogether satisfactory. For instance, the rod melts on the outside and flows away before softening adequately to allow mating surfaces of the plastic members to be pressed into contact with one another. Also, more rapid softening of the rod would be beneficial. In addition, the metal wire is sometimes undesirable in the welded product. Therefore, there is a need for an improved welding rod and welding method based thereon.